1. Field of the Invention
This invention relates to a control system for push-pull unit mounted on a motor scraper, and more particularly to a control system having an improved operational response characteristic which is provided with an electrically operating unit including therein solenoid valves so that the fluid under pressure delivered by a hydraulic pump can be supplied into either one of a bail actuating cylinder and suspension cylinders in accordance with the application without directing the fluid simultaneously into both the cylinders.
2. Description of the Prior Art
A motor scraper for use in scraping and leveling the ground is comprised of a drive vehicle body having an engine mounted thereon, and a bowl vehicle body having a scraper blade fitted in the lower part thereof and adapted to be loaded with the scraped earth and sand.
Usually, ground scraping and leveling operation can be carried out by one motor scraper; however, in case where comparatively stiff ground is scraped or leveled or in case of heavy scraping wherein a great deal of earth is scraped, two or more motor scrapers connected tandem are used for increasing the driving force. Therefore, each of the front and rear motor scrapers is provided with a push-pull unit adapted to form a pair with another unit mounted on the front part or rear part of another vehicle.
In the front part of the drive vehicle body, this push-pull unit includes a push block movably fitted to the vehicle body frame and a bail pivotally mounted on the push block so as to oscillate freely, whilst in the rear part of the bowl vehicle body a pushed block having a hook engageable with the bail is fixedly secured to the vehicle body frame.
Whilst, the bowl vehicle body of the motor scraper is provided with a suspension control system including a suspension cylinder for adjusting the height of the vehicle so that the vehicle height may be controlled in accordance with respective requirements when running, scraping earth and loading the scraped earth.
In the control systems of the kind specified, a hydraulic circuit for controlling the suspension control system which includes a flow divider has been used as a hydraulic circuit for the push-pull unit. As a result, the flow rate passing through the suspension controlling hydraulic circuit is reduced which gives a bad influence on the operational response characteristic. Further, since the control operation is made hydraulically, it is required to move the lever of the push-pull control valve manually. Therefore, it is necessary to provide a valve of a special type with a lever within a cabin of the vehicle, so that it is dangerous, and also a long hydraulic piping is required to be installed causing a high pressure loss which results in an increase in the load of the engine.
Further, in the prior art control systems, since the fluid is always relieved at a constant pressure at raised position of the bail, the engine load increases, and also provision of separate levers is required for push-pull control and suspension control, respectively, rendering their operation difficult.